Memories are briefly categorized into volatile memories such as an SRAM (Static Random Access Memory) and a DRAM (Dynamic Random Access Memory) and nonvolatile memories such as an EEPROM (Electrically Erasable Programmable Read Only Memory) and a flash EEPROM. A volatile memory has a disadvantage in that data is lost once the power source is turned OFF. On the other hand, a nonvolatile memory in which data is not lost even when the power source is turned OFF, is used for a program for running a system and the like.
In recent years, a nonvolatile memory used for an IC card is attracting attentions. A magnetic card that is presently used can be easily reprogrammed in data, which means it is low in security. Accordingly, an IC card is expected to be used as a medium substituting a magnetic card and to be applied to electronic money or resident cards. In particular, its function regarding the security of data is emphasized in order to avoid forgery and abuse.
Nonvolatile memories using semiconductors are categorized into a rewritable type using a memory element of a floating gate structure, a ferroelectric element, or a memory element that exhibits magneto resistance and phase change, and a non-rewritable type such as a mask ROM. Besides, there is another rewritable type which can be written only once, using a memory element of a floating gate structure and a memory element that exhibits phase change (hereinafter also referred to as an OTP (One-Time Programmable)) (see Patent Document 1).
[Patent Document 1]
Japanese Patent Laid-Open No. 2003-51196